I am attempting to correct an issue that has plagued me since setting up CiviCRM. The issue remains for me, even after upgrades. The issue is that on some pages within CiviCRM, the menu doesn't fully load, and ultimately renders a page useless. It occurs when I am going to the Civimail component and some other features. It isn't consistent. Here are two screenshots. The first shows the normal menu that appears on most pages. The second image is the image with the broken menu:
Sometimes it is worth visiting /civicrm/admin/menu?reset=1 and right clicking on any menu item, and then click Edit and Save so that you then get the message
Click here (/civicrm/admin/menu?reset=1) to reload the page and see your changes in the menu bar above.
Otherwise you can just visit that url directly. This may not help with your situation since it seems to be less consistent. But it may help others looking around for such advice